The present invention is directed to controlling operation of a processor device during startup of the processor device, and especially to reset supervisor apparatuses that await a stable supply signal in effecting such processor device control.
Often in operation of processor devices, and especially in processor devices in embedded systems, the power-up of the supply voltage is not a clean event. That is, the supply voltage is not sufficiently stable immediately after power-up to reliably operate a processor device. Such initial instability of supply voltage is especially present in battery operated systems because the insertion of a battery often causes significant ringing, “glitching” or other disadvantageous anomalies in the supply signal. An example of such noise on a supply line is illustrated in FIG. 1.
By way of further example, and not by way of limitation, in products with on-off switches contact bounce of the switch can also cause unclean power-up of the supply signal. If the power-up evolution involves too much noise or other signal anomalies a processor may experience a brownout condition. A brownout condition is generally considered to be an errant condition of the processor that requires a reset operation to be performed before the processor behaves as expected. The processor is sometimes said to be “lost” or “off in the weeds” during a brownout condition.
Some type of reset supervisor apparatus may be employed to control the reset pin of the processor to avoid a brownout condition. One such reset supervisor apparatus is a supply voltage supervisor (SVS) circuit that can hold the processor in a reset condition (i.e., reset the processor) until the supply voltage reaches a predetermined voltage. Such SVS circuits also reset the processor after the processor begins operation if the supply voltage dips below the predetermined voltage. A problem with prior art SVS circuits has been that the threshold level at which an SVS circuit operates often does not fit well with the system with which it is employed. For example, the predetermined threshold voltage may be lower than the minimum operating voltage of the processor monitored by the SVS circuit, or the predetermined threshold voltage may be higher than the desired operating voltage of the predetermined voltage or of the system within which the processor is included.
There is a need for an apparatus and method for controlling operation of a processor during startup that is independent of the level of the supply voltage provided to a processor device.
There is a need for an apparatus and method for controlling operation of a processor during startup that provides a reset to the processor based on stabilization of the supply voltage and not based on a predetermined threshold value.